This invention relates to printing presses, and more specifically to those of the rotary type including one or more inking rollers. Still more specifically, the invention pertains to a variable-amplitude vibrator for imparting end-to-end vibratory motion to an inking roller, or to each inking roller, in a printing press with a view to the creation of an ink film of constant thickness on the plate cylinder or cylinders.
Printing presses having inking rollers capable of endwise or axial vibration have been known and used extensively in the printing industry. In some such printing presses it is frequently practiced to deliver two or more inks of different colors to the separate, longitudinally divided sections of the plate cylinder from the inking rollers. This multiple-color printing method necessitates the employment of some measure to prevent the intermingling of the adjacent inks due to the endwise vibration of the inking rollers.
One of the known measures adopted for the above purpose, in cases where the images to be printed to different colors will always be in the same locations in the axial direction of the plate cylinder, is the formation of annular grooves between the adjacent roller and cylinder sections. If the image locations are subject to change from run to run, the use of ink scrapers has been common for scraping the inks off the safe surface regions between the different image areas. The widths of these surface regions, and the amplitude of vibration of the inking rollers, must of course be varied depending upon how close the image areas lie to each other.
Generally speaking, inking rollers should spread ink as far as possible to give beautiful prints. If circumstances permit, therefore, their vibratory motions should be of the maximum practical amplitude.
The foregoing considerations lead one to the conclusion that the amplitude of vibration of inking rollers must be adjustably variable in as many, and as fine, steps as possible. Most of conventional variable-amplitude vibrators used for the purpose in question, however, offer an inconveniently small number of steps of amplitude change.
Another problem with the prior art arises from the fact that a single variable-amplitude vibrator has been used for driving all the inking rollers in a printing press. Since the inking rollers vibrate in phase according to this conventional arrangement, excessive vibrations develop and travel to the other undesired parts of the press, thereby impairing its durability and actually lessening its useful life.